Wild roses belong to the genus Rosa (Family Rosaceae) and are mainly found across northern North America, urope and Asia, between 20 and 70 latitude with the centre of
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the genus in central and southwestern Asia (Krüssmann 1981). They are of the most common shrubs across Canada, extending from the U.S.A./Canada border north to the edge of the tree line.
Wild roses are erect, deciduous, perennial shrubs capable of clonal growth from underground rhizomes and tend to form thickets. Stems are usually bristly and armed with dense prickles (Soper and Heimburger 1982). Roses have prickles and not thorns, thorns being modified stems made from the same cells as the stem itself, whereas, prickles are comparable to hairs, sometimes being quite coarse, and are extensions of the epidermis and cortex. Leaves of roses are alternate and pinnately compound with five to seven serrate leaflets fused to the petiole for most of their length. Rose flowers are large, fragrant, and perfect with five parted, pink to red petals (Soper and Heimburger 1982). Flowers are usually borne singly or in groups of two or three, and generally bloom from late spring to early summer and are pollinated by insects. The fruits, known as hips, are red with a fleshy or pulpy receptacle surrounding the seeds, called achenes (Soper and Heimburger 1982). Seeds are hard, have stiff hairs along one side, and are resistant to damage by the digestive systems of the many vertebrates that feed on them. Hips are variable in shape (elliptic, globose, or pyriform) and often persist on plants throughout the winter (Soper and Heimburger 1982).
Wild roses are considered keystone species in many landscapes as they reinforce relationships with many other plants, mammals, birds and insects that inhabit the area (Shorthouse 2010). The fragrant flowers attract bees, flies and many beetles, not because of nectar (roses flowers are without nectaries), but rather the copious amounts of protein- rich pollen. Rose thickets also provide cover, nesting sites and protection for many
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species of wildlife. All above-ground parts are eaten by a variety of herbivores ranging from large mammals such as deer, bears, and moose that eat branches and hips, to insects occupying the leaf chewing, leaf sucking, leaf mining, and stem boring guilds
(Shorthouse 2010). Seeds do not germinate during the first spring because they must undergo warm stratification during the summer followed by cold stratification the second winter. After cold stratification, seeds germinate over a wide range of temperatures soon after snowmelt, taking advantage of early spring moisture and growing vigorously at low temperatures (Schori 2003).
Roses are well adapted to survival and dispersal in the harsh conditions of north temperate regions of the world (van Groenendael et al. 1997). Although the number of seeds is small, large seed size contributes to rapid production of a large root system. Plants then spread vegetatively by rhizomes over a wide area, forming clones that may persist for hundreds of years (van Groenendael et al. 1997). Although roses produce many fine roots in the top 20 cm of soil, deep roots may reach 140 cm (Strong and LaRoi 1986). Calmes and Zasada (1982) found rhizomes 20-30 cm below the surface. Rhizomes are protected at this depth allowing them to resprout following fire or other disturbances.
The genus Rosa is notoriously difficult and taxonomically complex (Bruneau et al. 2007) because of variability within species and the existence of multiple reproductive strategies, ranging from apomixis (replacement of normal reproduction by asexual reproduction) to hybridization and outcrossing (Lewis 1959; Wissemann 2003). In addition, they exhibit different modes of character inheritance such as intra-specific variability and polyploidy (Erlanson-MacFarlane 1966; Bruneau et al. 2007). The boundaries between species of
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wild roses have always been difficult to define because where some rose taxonomists saw polymorphism, others saw distinct species. Depending on the author, between 14 and 4000 species have been proposed; however, it is generally accepted that the genus consists of 150-200 morphospecies (Bruneau et al. 2007).
The taxonomic complexity of roses makes the genus a model in which simple concepts of radiation, speciation and taxonomy come to their limits. For example, the biological species concept is not applicable, as all species are inter-fertile and produce viable and fertile offspring (Wissemann and Ritz 2007). As a result, taxonomists of the genus Rosa apply two concepts of classification: a morphospecies-based system that focuses on morphological differentiation, and an evolutionary system which combines numerous sources of evidences including molecular data (Bruneau et al. 2007).
The genus Rosa has been divided into 10 sections (Wissemann 2003), three of which include roses that are found in Canada. The section Carolinae is composed of 5 species in North America, four of which (R. carolina L., R. nitida Willd., R. pulustris Marsh, R. virginiana Herrm.) occur in Canada. The section Cinnamomeae is composed of about 80 species in Asia, Europe and North America. Species found in Canada are R. acicularis, R. arkansana Porter, R. blanda, R. gymnocarpa Nutt. ex Torr. Et A. Gray, R. nutkana C. Presl., R. pisocarpa A. Gray and R. woodsii Lindl. Another rose in this section, R. rugosa Thunb. is endemic to Japan and was intentionally introduced into Canada as a garden plant and has since become feral in various regions. The section Synstylae is composed of approximately 25 species, however, only R. setigera Michx. is found in Canada. In
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50 species, R. rubigenosa L. and R. canina L., were introduced into Canada and have become feral in some areas. Species of wild rose found in Ontario are R. acicularis, R. blanda, R. pulustris, R. carolina, and R. setigera.
Most of the roses grown in the botanical gardens of the world come from wild roses in Asia, the same area where about 60% of domesticated flowers, fruit trees and vegetables originated (Krüssmann 1981; Cairns 2003). About eight species of Asian wild roses are the source of the domesticated shrubs that were altered by breeding and their flowers turned into the hundreds of varieties enjoyed in botanic gardens throughout North America and Europe, the former since ancient times (Cairns 2003). For the past two centuries, ornamental and cut flowers from such roses have become the centre of a multi- billion dollar horticultural industry of ornamental and cut flowers (Cairns 2003).
Domesticated roses are also a major source of essential oils for perfumes and their hips have been used for human food throughout recorded history (Cutler 2003).